1. Technical Field of the Invention
The present invention relates to a method for rerouting of calls in communication networks, as for instance GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunication System) networks with separated call control and bearer control. The invention further relates to a method to connect a further communication network with monolithic signalling, as for example an combination of C7 and ISUP (ISDN User Part) to a communication network with separated call control and bearer control.
2. Description of Related Art
Recently communication networks have been proposed that separate the call control and bearer control at least logically. For example the IETF draft SS7-Internet Engineering—Architectural Framework, published July 1998 introduces a concept for such a network architecture. However, the IETF draft includes only a rough concept of separating call control and bearer control.
The published concepts of connecting a further network with monolithic, that is not supporting a separation of call control and bearer control, signalling and a communication network with transport independent call control, that is a call control that is independent of the payload transmission, lead to the assumption that there is a one to one relation between interface means for the signalling and the interface means for the payload transmission. An one to one relation between these interface means forces signalling interface means of a communication network to interwork always with the same interface means for the payload connection, independent of call requirements. This means for example in a GSM network with separated call control and bearer control that is connected to a fixed network with ISDN signalling, that a signalling gateway must always link in the same media gateway for the payload transmission, independent from the incoming call being a voice or a data call. This leads to an inflexible architecture that does not take full advantage of the opportunities offered by the separation of call control and bearer control.
A further inflexibility is the lack of mechanisms that allow a change of the selected payload transmission devices without releasing a call.
Therefore, it is object of the invention to support a more flexible architecture based on the separation of call control and bearer control.
It is a further object of the invention to combine networks with monolithic signalling like a combination of ISUP and C7 to communication networks with transport independent call control.
It is also object of the invention to allow a higher flexibility in a network with separated call control and bearer control without changing existing signalling protocols.
Another object of the invention is to allow further assignments of already assigned radio access transmission devices.
It is advantageous that no change of existing protocols is necessary to implement the method. This reduces the costs and the time needed for the implementation. Especially advantageous is that the reassignment of an already assigned radio access network controller can be done without releasing the connection to a subscriber. This allows handling equipment failure without call interruption.
Very advantageous is according to claim 2 the use of the existing ISUP protocol, as this is a widespread protocol and therefore enables a large number of operators to easily make use of the invention.
Especially advantageous is according to claim 3 the use of different routes for the identification, by this an easy to handle differentiation is possible and the identification of the payload transmission device between a transit switch and a signalling interface is handled independent from the identification network internally.
Very advantageous is the identification of the devices by a destination or and originating point code according to claim 4. Firstly these codes are parameter that are already used in an initial address message, and secondly they are already used to identify devices. This reduces changes in the existing implementations when adapting it to the invention.
Further advantageous is the use of circuit identity codes according to claim 5 this also makes the identification handling in the network independent from the identification at the interface. Furthermore, an appointment of a circuit identity code has to be done anyway to set-up a connection. This saves some extra work during a network set up.
Very advantageous is the initiation of a reassignment by a different control node than the serving control node according to claim 7. This allows a detection of errors or an optimisation of a connection by different nodes.